Tongue and groove plywood panels are used commonly in the construction industry as sub-flooring panels. In the construction of a sub-floor, these panels span the distance between the floor joists of a building with the interlocking tongue and groove side edges of adjacent panels serving to support the panels against deflection between the joists while the end edges of the panels are located over and supported by the joists.
Applicant's Canadian Pat. No. 914,370 discloses a tongue and groove plywood panel of the type mentioned above. Canadian Pat. No. 914,370 discloses a tongue and groove arrangement in which the upper veneers of two adjacent panels are spaced slightly apart at the joint by virtue of a tongue that is slightly longer than the groove is deep. This arrangement allows for swelling of the plywood panel due to moisture. Such swelling often happens as it is common building practice to form the sub-flooring at an early stage in the erection of buildings so that the sub-flooring is exposed to rain and other weather conditions. If the adjacent panels are not spaced along the tongue and groove joint, any swelling of the panel tends to be borne by the butted edges of the joint causing a ridge to form in the top surface of the panel which must be sanded down or otherwise treated to avoid marring the final floor covering.
In applying the final floor covering, the space between the upper surfaces of adjacent panels is filled in by a filling agent or by the adhesive used in the application of the final covering in order to form a smooth base.